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IRAM 30m telescope flux measurement of Cyg X-3 during a major outburst

ATel #10257; Thomas Krichbaum (MPIfR, Bonn)
on 12 Apr 2017; 11:43 UT
Credential Certification: Thomas P. Krichbaum (tkrichbaum@mpifr-bonn.mpg.de)

Subjects: Radio, Millimeter, Binary, Transient

Referred to by ATel #: 10274

Following ATELs #10109, #10126, #10138 and #10252 we have measured the flux density of CygX-3 with the IRAM 30m telescope on Pico Veleta on April 6 and 7, 2017. The measurements were performed with the EMIR receiver at 98.5 GHz and 228.7 GHz. The measured fluxes are: April 6, 06h20 UT: 4.63+/-0.24 Jy (98.5 GHz) and 2.95+/-0.44 Jy (228.7) GHz, and on April 7, 10h00 UT: 4.01+/-0.10 Jy (98.5 GHz) and 2.96+/-0.26 Jy (228.7) GHz. The gain calibration factors derived from the measurement of Saturn, Neptune were 6.53 Jy/K at 98.5 GHZ and 8.17 Jy/K at 228.7 GHz. We note to good agreement of the measured 1mm flux at 228 GHz with a near in time measurement of the SMA at 220 GHz (ATEL #10252, S=3.09+/-0.15 Jy on Apr. 7, 17.05 UT). From the measured flux densities we calculate a spectral index alfa (S ~ nu^alfa) of alfa = -(0.36 +/- 0.11), between 98.5 and 228.7 GHz, which indicates a mildly steep synchrotron spectrum, which is expected to further decay during the course of this outburst. The steep spectrum also indicates that the synchrotron turnover frequency is at or below 98.5 GHz. Further flux density monitoring in the mm- and radio-bands is encouraged.